I referred you to, "Wotnext," a South African KLR650 rider who's ridden both in Africa and in the Americas (45,000 miles in the latter venue), who modified his bike extensively for the camping equipment load.
He might respond to your Adventure Rider "conversation," or, if not . . . perhaps I can develop his e-mail address for you; PM me if you want to exploit that possibility.
The stronger springs you suggest (Progressive front and whatever alphabet soup rear suggested) sound like an improvement for your own weight and extra gear you propose carrying; however . . . the finesse of, for example, a Cogent Suspensions Moab rear shock, stiffer front springs and cartridge dampers remains wanting with such modifications only. The DAMPING/REBOUND of the stronger springs you propose does not keep pace with their greater spring rate.
Big deal? Maybe not. A lot depends upon your riding style and environment.
That said, I think your South African dealer offers sound (and economical) suspension upgrade for your mission; perhaps adequate in front-and-rear spring rate, but damping/rebound? Not so much.
Best wishes, whatever you decide, and . . . if your new KLR650 is a 2014-1/2 (or later) New Edition (with stronger suspension than previous models factory stock, and wider saddle), you can probably complete your journey with the bike as-built, stock, "out-of-the-box." I think Peter ("Wotnext," Riding Through the Americas, http://advrider.com/index.php?thread...ericas.970477/
) could have completed his odyssey with a stock bike, also.